This invention is directed in general to developer stations for reproduction apparatus, and more particularly to an improved electrostatographic reproduction apparatus developer station wherein the transport mechanism readily meters a desirable amount of developer material to the magnetic brush applicator without material compaction.
In electrostatographic reproduction apparatus, it is general practice to apply a uniform electrostatic charge to a dielectric member and modify such charge to form a charge patterrn corresponding in image-wise fashion to information to be reproduced. The charge pattern is then developed by applying pigmented marking particles to the dielectric member. The particles, which are charged to a polarity opposite to that of the charge pattern on the dielectric member, adhere to the pattern to form a developed image on the dielectric member. The developed image is then fixed to the dielectric member, or transferred to a final receiver member and fixed thereto by heat and/or pressure for example.
One common type of electrostatographic reproduction apparatus developer station in use today is the magnetic brush developer station. Such station includes a housing providing a reservoir for a supply of developer material. The developer material may be, for example, two-component material comprising magnetic carrier particles and relatively smaller pigmented marking particles. A mechanism, such as a paddle wheel, auger or ribbon blender, is located in the reservoir and serves to stir the carrier particles and marking particle to triboelectrically charge the particles so that the marking particles adhere to the surface of the carrier particles. A transport mechanism brings the developer material into the field of a plurality of magnets which, in turn, apply the marking particles to the charge pattern on the dielectric member.
A typical transport mechanism includes a roller having a plurality of buckets located about its peripheral surface. As the roller is rotated, the buckets scoop up developer material and deliver the material to the magnetic brush (see for example U.S. Pat. No. 4,716,437, issued Dec. 29, 1987 in the name of MacLellan). While such transport mechanism has poven generally successful in operation, its arrangement may lead to several problems. Transfer of developer material from the transport mechanism to the magnetic brush may require a magnetic field of a strength which adversely effects subsequent transfer of marking particles to the charge pattern bearing member. Additionally, as the roller rotates the buckets in the developer station housing, developer material may be compacted into flakes which can cause serious image defects if applied to the charge pattern being developed.